WEBVTT - Why Do People Forget Memories? 0:00:00.200 --> 0:00:02.400 Hey, please take a second and leave us a review 0:00:02.480 --> 0:00:06.279 on Apple Podcasts, Spotify, or wherever you listen to the podcast. 0:00:06.960 --> 0:00:10.840 Thanks a lot. Hey, welcome to sign Stuff, a production 0:00:11.000 --> 0:00:16.160 of iHeartRadio I'm More cham and today we're looking into amnesia. 0:00:16.239 --> 0:00:18.720 How does it happen, why does it happen, and what 0:00:18.760 --> 0:00:21.959 are some of the most dramatic cases of it in history. 0:00:22.520 --> 0:00:24.840 It's part of a two part series on memory. So 0:00:24.960 --> 0:00:28.120 if you haven't checked out the first episode about super memory, 0:00:28.440 --> 0:00:30.880 go check it out. But in this episode, we're going 0:00:30.920 --> 0:00:33.599 to explore what it means to edge and then erase 0:00:34.000 --> 0:00:36.960 a memory. We're going to learn about a new technology 0:00:36.960 --> 0:00:40.680 that can essentially suppress memories with the push of a button. 0:00:41.000 --> 0:00:43.360 And we're going to look into amnesia and a condition 0:00:43.520 --> 0:00:49.080 called severely deficient autobiographical memory, which once you hear about it, 0:00:49.320 --> 0:00:52.040 you won't be able to forget. So tie a stringer 0:00:52.080 --> 0:00:55.080 on your finger because we are going down a memory 0:00:55.120 --> 0:01:04.200 hole to explore the science of amnesia. Enjoy. Hey everyone, 0:01:04.760 --> 0:01:09.240 Today we're continuing our exploration of memory. In the previous episode, 0:01:09.360 --> 0:01:12.280 we talked about the ability to remember a lot of things, 0:01:12.600 --> 0:01:16.520 and now we're going to focus on we'regetting for example, 0:01:16.640 --> 0:01:19.080 have you ever wondered what happens to a memory once 0:01:19.120 --> 0:01:23.040 you can't remember it anymore? Or why sometimes, usually in 0:01:23.080 --> 0:01:26.160 the worst possible moment, you can't remember an important piece 0:01:26.200 --> 0:01:29.320 of information like your friend's name when you're introducing them 0:01:29.360 --> 0:01:32.600 at a party. And then going further, what's actually happening 0:01:32.640 --> 0:01:36.640 in people with amnesia or people who can't make new memories. 0:01:37.240 --> 0:01:40.200 Have you seen the movie Memento or remember the character 0:01:40.240 --> 0:01:44.200 of Dori and finding Nemo. Well, that actually happens in 0:01:44.240 --> 0:01:47.120 real people. What's it like to be them and how 0:01:47.160 --> 0:01:49.800 are they still able to function? We're going to tackle 0:01:49.840 --> 0:01:52.720 all of these questions, starting with how memories are made 0:01:53.280 --> 0:01:56.440 and how they're forgotten to tell us about the search 0:01:56.480 --> 0:01:59.720 for the basic mechanism of memory. Talk to doctor Sarah 0:01:59.800 --> 0:02:02.760 ro bin, a professor and the co director of the 0:02:02.800 --> 0:02:08.919 Cognition Agency and Intelligence Center at Purdue University. Well, thank you, 0:02:08.960 --> 0:02:10.280 doctor Robbins for joining us. 0:02:10.720 --> 0:02:13.520 Yes, thank you for having me. I am Sarah Robbins. 0:02:13.600 --> 0:02:16.880 I'm a philosopher and cognitive scientist of memory. So I 0:02:16.919 --> 0:02:19.040 study and in particular the science of memory. 0:02:19.320 --> 0:02:22.600 That's good that you remember all that I. 0:02:22.639 --> 0:02:24.640 No longer have to write it down takes a little bit. 0:02:26.160 --> 0:02:31.040 So that's an interesting mix between psychology and philosophy. Can 0:02:31.080 --> 0:02:33.480 you tell us a little bit about that area in between. 0:02:33.880 --> 0:02:36.720 Yeah, and it includes neuroscience very deeply as well, So 0:02:36.760 --> 0:02:39.200 I think of it as sort of different ways of 0:02:39.400 --> 0:02:42.760 researching and thinking about the mind and the brain. Historically 0:02:42.960 --> 0:02:47.160 they were very intertwined, so early psychology was often called 0:02:47.240 --> 0:02:51.359 natural philosophy, and I often see the philosopher's role as 0:02:51.360 --> 0:02:53.800 someone who's paying attention to what every one of those 0:02:54.040 --> 0:02:56.760 is doing and talking about the bigger questions that started 0:02:56.760 --> 0:02:57.959 the science in the first place. 0:02:58.040 --> 0:03:00.400 Feels a little like inceptions. It's like your researching what 0:03:00.520 --> 0:03:03.200 we think of, how we think about, what we're learning about, 0:03:03.200 --> 0:03:03.600 how we. 0:03:03.520 --> 0:03:06.560 Think, yes, exactly, that's fun. 0:03:08.720 --> 0:03:11.440 Okay. According to doctor Robins, scientists have been trying to 0:03:11.440 --> 0:03:14.960 figure out how the brain records memories for a long time. 0:03:15.400 --> 0:03:18.600 It's been a search for what scientists call the n gram. 0:03:19.520 --> 0:03:23.160 So an ingram is really the neural mechanism that makes 0:03:23.240 --> 0:03:26.920 remember impossible or by which memories are supported so that 0:03:27.000 --> 0:03:28.760 they can later be remembered. 0:03:29.160 --> 0:03:33.960 Okay, like how the brain stores information? Yeah, and I 0:03:33.960 --> 0:03:36.480 guess for a long time people have been wondering like, 0:03:36.520 --> 0:03:37.680 how does that work in the brain? 0:03:37.960 --> 0:03:40.440 Exactly? Yeah, how is it? Where is it? Like what 0:03:40.680 --> 0:03:44.080 could possibly be the case? So the zoologists that coined 0:03:44.120 --> 0:03:47.040 the term, Richard Demmon, she first wrote the book where 0:03:47.040 --> 0:03:49.600 he coined the term in nineteen oh four in German. 0:03:50.000 --> 0:03:52.640 He's calling it like it's somewhere in the irritable substance, 0:03:52.840 --> 0:03:55.680 which is how people thought about the kind of material 0:03:55.800 --> 0:03:58.320 of the brain at the time, which I just disagree. 0:03:59.080 --> 0:04:02.400 That's well, unfortunately I have a lot of irritable substance 0:04:02.480 --> 0:04:06.080 in my brain we all, especially in the mornings. 0:04:06.640 --> 0:04:08.840 Yes, it's especially irritable. 0:04:08.880 --> 0:04:09.960 Then, absolutely there. 0:04:11.680 --> 0:04:14.640 So we've been looking for how the brain stores memories 0:04:14.800 --> 0:04:18.400 for over a hundred years now. You might think, why 0:04:18.440 --> 0:04:20.880 has it taken so long? Can we just open up 0:04:20.920 --> 0:04:24.640 a brain and see what's going on? Well, it's not 0:04:24.800 --> 0:04:25.359 that easy. 0:04:27.040 --> 0:04:29.159 One is a challenge that is, like it's hard to 0:04:29.200 --> 0:04:32.720 know what's in your memory outside of actually like being 0:04:32.720 --> 0:04:34.520 able to look in there. Right, So if you can't 0:04:34.560 --> 0:04:36.760 remember something, it's kind of a question of like is 0:04:36.760 --> 0:04:38.400 it in there but you can't get it out? 0:04:38.920 --> 0:04:40.159 Or is it not in there? 0:04:40.400 --> 0:04:43.200 But like how do you tell Like how do we 0:04:43.279 --> 0:04:45.680 know what's really in there until we get it out. 0:04:46.000 --> 0:04:49.239 Yeah, it just made me realize what a difficult problem 0:04:49.279 --> 0:04:52.479 this is because I think we're all familiar with memories. 0:04:52.520 --> 0:04:55.800 We all have memories, we all remember things, but like, 0:04:55.839 --> 0:04:57.800 how do you do an experiment on to figure out 0:04:57.839 --> 0:04:59.960 how it works inside a brain as it's happening. 0:05:00.200 --> 0:05:03.080 Absolutely, And I think that's why some of these memories, 0:05:03.560 --> 0:05:05.360 like when they come to you kind of out of nowhere, 0:05:05.400 --> 0:05:07.640 are so delightful. Like when you hear a song you 0:05:07.680 --> 0:05:10.240 haven't heard for twenty years and you remember all the word. 0:05:10.320 --> 0:05:12.080 You can have this kind of like oh my gosh 0:05:12.240 --> 0:05:14.560 sort of reaction to that. Oh it was in there, 0:05:14.560 --> 0:05:18.320 and you sort of had no idea that it was there. Right, 0:05:18.360 --> 0:05:20.080 It's not like I can like, oh, what other fun 0:05:20.120 --> 0:05:22.840 stuff isn't there? Like I'm not going to know until 0:05:22.880 --> 0:05:24.120 that happens again. 0:05:24.440 --> 0:05:28.039 Yeah, that is so tricky. In other words, it's hard 0:05:28.040 --> 0:05:31.239 to study how the brain stores memories because you can't 0:05:31.279 --> 0:05:34.520 just poke around someone's brain while they're making a memory 0:05:34.800 --> 0:05:37.799 or trying to remember something. But all of that changed 0:05:37.880 --> 0:05:41.159 about ten to fifteen years ago with the development of 0:05:41.200 --> 0:05:46.599 a technology called optogenetics. I'll explain what that technology is 0:05:46.680 --> 0:05:50.040 a little later. But first, here's what we've learned after 0:05:50.080 --> 0:05:54.360 a century of science, but how the brain records a memory. 0:05:55.120 --> 0:05:58.480 So you wrote in a paper that we found the nngram. 0:05:58.600 --> 0:05:59.920 What does that mean that we've found it? 0:06:00.000 --> 0:06:02.279 I think it's now the case that it's possible to 0:06:02.480 --> 0:06:06.719 identify the set of neurons that are active in storing memories. 0:06:06.960 --> 0:06:09.960 We'll step me through this. So I am walking around 0:06:10.240 --> 0:06:12.960 and something incredible happens. The unicorn jumps out of the 0:06:13.160 --> 0:06:16.320 manhole and then grows wings and flies off into the sky. 0:06:16.800 --> 0:06:19.960 I'm definitely going to remember that. What's happening in my brain? 0:06:20.920 --> 0:06:23.120 Yes, So what's happening? 0:06:23.200 --> 0:06:25.760 I mean, I'll give you a second to process that image. 0:06:25.760 --> 0:06:26.080 I just. 0:06:27.680 --> 0:06:30.200 Well, the unicorn area of processing and the manual air 0:06:30.279 --> 0:06:32.800 and not there yet. So there's a set of cells 0:06:32.880 --> 0:06:36.599 in the hippocampus and surrounding structures that are kind of 0:06:36.640 --> 0:06:39.960 responsible for being the ones that react to that experience 0:06:40.000 --> 0:06:42.920 and kind of encode information about that experience in somewhay, 0:06:43.120 --> 0:06:44.840 there's a whole lot of neurons in that area, and 0:06:44.880 --> 0:06:46.440 a subset of them are going to say, like we've 0:06:46.440 --> 0:06:48.760 got this one here. You know, we're going to take 0:06:48.800 --> 0:06:51.160 hold of that and something about the way that they 0:06:51.200 --> 0:06:54.680 activate together capture something about that events. 0:06:54.839 --> 0:06:57.320 All right, So I see the unicorn. There are some 0:06:57.520 --> 0:07:01.159 cells among the many, many, many many in my hippocampus 0:07:01.160 --> 0:07:03.200 that are like I'm ready, I'm ready to remember things. 0:07:03.400 --> 0:07:06.760 And then I see the unicorn. And it's what happens 0:07:06.800 --> 0:07:09.880 to those cells. They sort of like change, they something 0:07:10.520 --> 0:07:11.560 what happens. 0:07:11.360 --> 0:07:15.040 So they like become better connected to each other. I'm 0:07:15.040 --> 0:07:16.960 not sure how far I can go with this metaphor, 0:07:17.040 --> 0:07:20.280 but this is just like a sea of willing people 0:07:20.320 --> 0:07:22.600 to play on the team for whatever sport you have. 0:07:22.960 --> 0:07:25.240 Each time there's an experience, you like send a team 0:07:25.280 --> 0:07:28.480 out and like they play together and they kind of 0:07:28.480 --> 0:07:30.880 form a bond that makes them a team that is 0:07:30.920 --> 0:07:31.960 about the experience. 0:07:32.040 --> 0:07:34.840 They lock hands, they're like, we got this memory. We're 0:07:34.880 --> 0:07:37.480 going to remember that unicorn. We are the unicorn in 0:07:37.520 --> 0:07:37.840 your head. 0:07:38.000 --> 0:07:39.920 We got it exactly. And then they kind of go 0:07:40.000 --> 0:07:41.640 back into the sea and you bring out a new 0:07:41.680 --> 0:07:44.480 set to play the next game and they do their connecting. 0:07:45.600 --> 0:07:48.480 So that, in a nutshell, is what we know about 0:07:48.480 --> 0:07:51.440 how the brain records a memory, or at least a 0:07:51.480 --> 0:07:54.440 memory of an event. There's an area in your brain 0:07:54.640 --> 0:07:57.720 called the hippocampus, which sort of looks like two small 0:07:57.840 --> 0:08:01.920 jalapeno peppers buried deep inside your with millions of neurons 0:08:01.960 --> 0:08:05.119 in it, all connected to each other. And when something 0:08:05.200 --> 0:08:08.720 memorable happens, some of those neurons, maybe a few hundred 0:08:08.800 --> 0:08:11.600 of them, kind of get activated and they step up 0:08:11.840 --> 0:08:15.120 to remember the event, and they do it by strengthening 0:08:15.160 --> 0:08:20.000 the connections between them, which are called synopsis. The synopsis 0:08:20.040 --> 0:08:23.160 get stronger, which means that network of cells is more 0:08:23.320 --> 0:08:27.000 likely to activate together. As doctor Robin said, a good 0:08:27.040 --> 0:08:30.160 analogy is to imagine a stadium full of people, and 0:08:30.200 --> 0:08:33.000 when a new memory has to be recorded, as subset 0:08:33.080 --> 0:08:36.240 of those people step up and they lock hands and 0:08:36.280 --> 0:08:41.000 somehow that stores the memory. Okay, two quick things about that. First, 0:08:41.160 --> 0:08:44.439 a neuron can be a part of multiple memories, not 0:08:44.600 --> 0:08:44.960 just one. 0:08:46.640 --> 0:08:48.960 And it's possible over time that some of these cells 0:08:49.000 --> 0:08:50.800 will play on different teams. 0:08:51.640 --> 0:08:54.480 Right, It's like I'm the unicorn cell with these group 0:08:54.559 --> 0:08:57.120 of cells, but with these group of cells, I am 0:08:57.280 --> 0:09:02.000 the I am the purple crocodile, or is another. 0:09:01.760 --> 0:09:04.800 Day exactly exactly And. 0:09:04.720 --> 0:09:07.880 Two that's what we see happening in the hippocampus during 0:09:07.880 --> 0:09:10.520 an event, but we don't actually know if that's where 0:09:10.520 --> 0:09:13.880 the memory is stored. Is a hippocampus kind of like 0:09:13.920 --> 0:09:16.199 the hard drive of the brain, or is it more 0:09:16.280 --> 0:09:19.080 like the relay of the brain, or like what's happening? 0:09:19.800 --> 0:09:21.560 I think that's a question of live debate. 0:09:21.760 --> 0:09:25.240 So it could be that it's individually storing each memory 0:09:25.280 --> 0:09:28.120 and holding them and they stay in the hippocampus long term. 0:09:28.320 --> 0:09:30.400 That is a view that some people hold. It could 0:09:30.400 --> 0:09:32.200 be that it is just kind of a relay, like 0:09:32.280 --> 0:09:35.440 it's the place that keeps tags or recipes, right, but 0:09:35.520 --> 0:09:38.000 all the content is distributed elsewhere. 0:09:38.920 --> 0:09:41.559 Okay, that's what we know about how memories are formed. 0:09:42.000 --> 0:09:45.679 Now the question is how do memories get forgotten and 0:09:45.840 --> 0:09:49.000 what's happening in people with amnesia. We'll get to that, 0:09:49.400 --> 0:09:51.640 but first I wanted to dig deeper into how we 0:09:51.760 --> 0:09:55.040 know this is how memories are formed, because the answer 0:09:55.160 --> 0:10:01.439 is pretty cool. It involves a fairly recent technology called optogenetics, 0:10:01.640 --> 0:10:05.640 which basically lets you control memories with the push of 0:10:05.720 --> 0:10:06.319 a button. 0:10:07.880 --> 0:10:10.559 And so that's changed in the last few decades thanks 0:10:10.600 --> 0:10:14.320 to a range of sort of technological tool innovations. A 0:10:14.360 --> 0:10:18.240 central one of which is something called optogenetics, which is 0:10:18.320 --> 0:10:24.240 a technique for making neurons responsive to light. So, colloquially speaking, 0:10:24.559 --> 0:10:27.040 you're putting a light switch on neurons. You make it 0:10:27.080 --> 0:10:29.320 so that you can turn them on and off in 0:10:29.360 --> 0:10:34.920 a living, behaving organism. So you can make certain neurons 0:10:35.000 --> 0:10:37.960 fire action potentials, make them active, or you can inhibit 0:10:37.960 --> 0:10:43.560 them keep them from firing action potentials. Wow, it's incredible. 0:10:44.440 --> 0:10:46.800 Okay, we can probably spend the whole episode just on 0:10:46.840 --> 0:10:51.959 this technology because it's pretty wild. Basically, scientists can now 0:10:52.120 --> 0:10:55.080 hack into the DNA of neurons and make it so 0:10:55.120 --> 0:10:58.640 that when the neurons are activated, they produce a protein 0:10:58.679 --> 0:11:02.520 that makes the neurons sensitive to light, and scientists can 0:11:02.600 --> 0:11:05.360 time when this happens so that it only happens to 0:11:05.480 --> 0:11:10.720 neurons in a specific brain area and during a specific event. So, 0:11:10.800 --> 0:11:13.120 for example, you could make it so that everything you 0:11:13.200 --> 0:11:16.800 experience in the next hour or so gets etched into 0:11:16.840 --> 0:11:20.320 neurons in your hippocampus, and any neurons that get recruited 0:11:20.360 --> 0:11:25.199 to remember those memories become light sensitive to you. Nothing 0:11:25.200 --> 0:11:27.760 would change, You would simply have that memory as you 0:11:27.840 --> 0:11:30.760 normally would. But now if I take a tiny fiber 0:11:30.760 --> 0:11:33.840 optic flashlight and I thread it into your brain and 0:11:33.920 --> 0:11:37.120 turn the light on. Those neurons that recorded that memory 0:11:37.360 --> 0:11:42.520 would turn on and you would suddenly and involuntarily get 0:11:42.559 --> 0:11:45.680 a flashback of what happened. And if you press the 0:11:45.679 --> 0:11:49.520 button again, those neurons would activate again and you would 0:11:49.559 --> 0:11:53.959 get a flashback again. Essentially, you could relive that memory 0:11:54.080 --> 0:11:57.640 by just pressing that bun and scientists can also do 0:11:57.760 --> 0:12:01.320 the reverse, which is to make to produced proteins that 0:12:01.400 --> 0:12:05.040 make them stop working when they sense light. So you 0:12:05.080 --> 0:12:08.040 could do the opposite, which is to make a memory 0:12:08.280 --> 0:12:11.520 and then suppress that memory by simply turning on the light. 0:12:12.240 --> 0:12:14.800 The scientists could make you forget something you just saw 0:12:15.040 --> 0:12:19.000 by simply pushing on a button. It's pretty wild stuff, 0:12:19.320 --> 0:12:22.480 and it involves things like immediate early genes and special 0:12:22.559 --> 0:12:25.880 antibiotics to suppress these genes, which we don't have time 0:12:25.920 --> 0:12:28.840 to cover this, but this is essentially what has unlocked 0:12:28.840 --> 0:12:31.920 a lot of the memory research in the last ten years. 0:12:34.640 --> 0:12:36.880 I didn't know we were that advance in this kind 0:12:36.920 --> 0:12:39.199 of manipulation of neural activity. 0:12:39.520 --> 0:12:42.880 It's absolutely incredible to see what sorts of work could 0:12:42.920 --> 0:12:44.840 be done in this way. And there are people that 0:12:44.880 --> 0:12:47.080 have been using these similar techniques to sort of figure 0:12:47.080 --> 0:12:48.840 out which neurons are trying to be a part of 0:12:48.880 --> 0:12:50.800 the memory, and you can kind of follow them around 0:12:50.880 --> 0:12:53.199 and again find the ngram in this way and then 0:12:53.400 --> 0:12:54.719 activate and manipulate it. 0:12:55.840 --> 0:12:59.240 Okay, that is how we make memories. When we come back, 0:12:59.320 --> 0:13:02.000 we'll get to the ession of how we forget memories 0:13:02.360 --> 0:13:04.640 and what's happening in the brain of people with amnesia 0:13:05.120 --> 0:13:10.280 and something called severely deficient autobiographical memory. We'll get to 0:13:10.320 --> 0:13:13.560 all of that, So don't blink out. Lock in this memory. 0:13:14.160 --> 0:13:29.200 We'll be right back. Hey, welcome back. We're talking about 0:13:29.240 --> 0:13:32.360 the size of amnesia, and so far we've talked about 0:13:32.360 --> 0:13:35.280 how the brain makes memories. Now we're going to talk 0:13:35.280 --> 0:13:38.960 about how the brain forgets memories. As it turns out, 0:13:39.040 --> 0:13:42.160 there's a big mystery about how we actually forget that 0:13:42.320 --> 0:13:45.040 scientists haven't figured it out. To take us through this, 0:13:45.280 --> 0:13:49.559 here's doctor DANIELA. Palombo, Professor of psychology at the University 0:13:49.600 --> 0:13:53.840 of British Columbia. Well, thank you doctor Palombo for joining 0:13:53.920 --> 0:13:54.319 us again. 0:13:54.600 --> 0:13:55.559 Yeah, my pleasure. 0:13:55.800 --> 0:13:58.440 So I thought it'd be interesting to talk about the 0:13:58.480 --> 0:14:00.840 absence of memories what are some of the different ways 0:14:00.880 --> 0:14:02.440 that we can lose memories. 0:14:02.720 --> 0:14:05.360 Yeah, that's a really good question. So I guess I'll 0:14:05.400 --> 0:14:08.280 start by saying that any of us can lose our memories. 0:14:09.280 --> 0:14:12.520 Okay. According to doctor Palombo, there are several kinds of 0:14:12.679 --> 0:14:16.440 memory loss. First is the casual kind that we all 0:14:16.520 --> 0:14:19.440 experience every day in our memory slips. 0:14:20.560 --> 0:14:23.240 So in our day to day lives, you know, whether 0:14:23.280 --> 0:14:26.680 we're young or older, we see that we experience memory 0:14:26.680 --> 0:14:29.840 slips where we think we should have access to something 0:14:29.880 --> 0:14:32.480 we don't, and that happens to all of us all 0:14:32.520 --> 0:14:34.960 the time. I'm sure you've experienced this many times. And 0:14:35.080 --> 0:14:37.840 so I have a very vivid memory of a time 0:14:37.880 --> 0:14:39.960 where I was introducing a bunch of people at a 0:14:39.960 --> 0:14:42.920 party and I had a coworker over who I knew 0:14:43.040 --> 0:14:47.320 very well, and I just temporarily forgot my coworkers seeing 0:14:48.000 --> 0:14:50.640 and he was staring at me in shock and disbelief, 0:14:50.760 --> 0:14:56.080 and I was also very very surprised and embarrassed, and 0:14:56.120 --> 0:14:58.080 then you know, a few minutes later, it popped back 0:14:58.120 --> 0:15:01.960 into my mind. So that type of loss refers to 0:15:02.600 --> 0:15:06.920 temporary and access to information, and it certainly happens as 0:15:06.920 --> 0:15:09.640 we get older and This is all part of healthy aging. 0:15:09.960 --> 0:15:11.760 I see, are you still friends with this person or 0:15:12.360 --> 0:15:14.560 that relationship? 0:15:14.640 --> 0:15:16.200 They did forgive me thanks leady. 0:15:16.640 --> 0:15:19.600 They forgot about it. Well, this makes the question about 0:15:19.720 --> 0:15:22.320 in the situations where we can get at a memory, 0:15:22.320 --> 0:15:25.880 but later on we remember, like what happens there? Like 0:15:25.920 --> 0:15:27.840 where does that memory go that I can't excess it? 0:15:28.240 --> 0:15:31.280 So sometimes it's simply due to interference. So we're in 0:15:31.320 --> 0:15:34.320 a situation where we're just not searching for the memory 0:15:34.360 --> 0:15:36.840 in the right way, and then later on something in 0:15:36.880 --> 0:15:40.880 our environment might trigger that memory. Sometimes it's because we're 0:15:41.040 --> 0:15:44.160 feeling very stressed. It can be feeling a bit anxious 0:15:44.160 --> 0:15:44.720 in the moment. 0:15:45.640 --> 0:15:49.200 So that's a memory slip where we have temporary trouble 0:15:49.440 --> 0:15:53.800 accessing a memory. There's also just forgetting something over time. 0:15:55.560 --> 0:15:59.160 Is there just plain forgetting? Like is it possible for 0:15:59.520 --> 0:16:01.880 me to have stored a memory in my brain cells 0:16:02.000 --> 0:16:04.480 but over time they just sort of, you know, like 0:16:04.520 --> 0:16:07.080 the hard drive gets corrupted or erased. 0:16:07.320 --> 0:16:11.000 Yes, so forgetting is a pretty loaded term. But you're 0:16:11.120 --> 0:16:13.640 right that we can form memories and then over time 0:16:13.760 --> 0:16:18.440 those memories become difficult to access. And one hypothesis is 0:16:18.440 --> 0:16:22.240 that that's because there's lots of interfering new information that 0:16:22.280 --> 0:16:25.440 we're encoding and needing to retrieve, and so the more 0:16:25.480 --> 0:16:28.840 memories we form over our lifetime, the more competition there is. 0:16:29.160 --> 0:16:29.360 Right. 0:16:29.960 --> 0:16:33.400 Another hypothesis is that just as our lives change and 0:16:33.440 --> 0:16:36.280 we grow, et cetera, the retrieval cues that we use 0:16:36.360 --> 0:16:40.120 to access those really old memories are not as close 0:16:40.160 --> 0:16:44.040 to our fingertips anymore. So you've moved on from your 0:16:44.120 --> 0:16:48.000 childhood home, et cetera, so it's harder to access those memories. 0:16:48.600 --> 0:16:52.040 I see, you sort of lose the path to those memories. 0:16:52.200 --> 0:16:53.120 Yeah, exactly. 0:16:54.880 --> 0:16:57.120 So some things you can lose a memory because you 0:16:57.160 --> 0:16:59.560 lose a connection to it. It's still in your brain, 0:16:59.680 --> 0:17:02.720 but because it's simply not relevant to you, you never 0:17:02.760 --> 0:17:06.080 find your way to it again. Now, memory slips and 0:17:06.160 --> 0:17:10.600 losing connections to your memories over time are both natural processes. 0:17:10.880 --> 0:17:13.240 They happen to anyone. But now we get to the 0:17:13.320 --> 0:17:17.399 kind of memory loss that's due to something specific. 0:17:17.920 --> 0:17:21.119 And that can happen in the context of disease. So 0:17:21.200 --> 0:17:25.440 you've probably heard about different forms of dementia, like Alzheimer's disease, 0:17:25.880 --> 0:17:30.800 where you can see quite profound, albeit progressive memory loss. 0:17:31.560 --> 0:17:35.040 And then there's another condition called amnesia. Then this is 0:17:35.119 --> 0:17:38.240 often due to a brain injury of virus. It can 0:17:38.320 --> 0:17:41.720 happen in the context of a stroke, and here. 0:17:41.560 --> 0:17:44.600 We get to amnesia. Now, the thing about amnesia is 0:17:44.600 --> 0:17:48.040 that it typically happens because of an event. It could 0:17:48.040 --> 0:17:51.200 be a stroke or a traumatic brain injury, or sometimes 0:17:51.240 --> 0:17:54.960 it's a virus that infects your brain. Whatever the cause, 0:17:55.200 --> 0:17:58.120 most cases of amnesia have something in common. 0:17:59.400 --> 0:18:02.760 Yeah, lots of different causes to amnesia, but one thing 0:18:02.880 --> 0:18:06.040 that they have in common is that they affect really 0:18:06.160 --> 0:18:08.600 similar networks in the brain. And there's one area of 0:18:08.600 --> 0:18:12.320 the brain in particular that's quite vulnerable to whether it's 0:18:12.359 --> 0:18:15.920 a virus or certain kinds of stroke, certain kinds of 0:18:15.960 --> 0:18:19.280 traumatic brain injury, et cetera, epilepsy, and that's a region 0:18:19.280 --> 0:18:22.199 of the brain called the hippocampus. And so when that 0:18:22.359 --> 0:18:25.200 area of the brain is affected, regardless of the cause, 0:18:25.640 --> 0:18:28.080 you see a profound loss of memory. 0:18:30.840 --> 0:18:33.560 Yes, the thing most cases when anesia have in common 0:18:33.800 --> 0:18:37.320 is that they affect the hippok campus. Now, once the 0:18:37.400 --> 0:18:41.720 hippocampus's damaged, two basic things can happen. One, you can 0:18:41.760 --> 0:18:45.199 lose past memories that you had before the event the 0:18:45.320 --> 0:18:49.800 damage to hippocampus. For example, childhood memories, the names of people, 0:18:50.240 --> 0:18:53.760 those could all be gone. And two, you can also 0:18:53.840 --> 0:18:57.560 lose the ability to make new memories after the event, 0:18:58.200 --> 0:19:01.240 and both of these kinds of anesia have different names. 0:19:01.640 --> 0:19:06.240 Using memories you had before the event is called retrograde anesia, 0:19:06.400 --> 0:19:09.399 and losing the ability to make new memories is called 0:19:09.800 --> 0:19:14.200 terograde anesia. You're probably familiar with these kinds of anesia 0:19:14.320 --> 0:19:17.639 just from popular culture. In a soap opera, when someone 0:19:17.680 --> 0:19:20.160 has an accident and they can't remember who they are 0:19:20.280 --> 0:19:24.399 or anything about their history, that's retrograde anesia. And in 0:19:24.440 --> 0:19:28.040 the movie Memento or with Dory and Finding Nemo, where 0:19:28.040 --> 0:19:30.880 the character seems to forget everything that happens to them 0:19:31.040 --> 0:19:36.320 and everything seems new to them, that's anterograde anesia. Now, 0:19:36.359 --> 0:19:38.760 there are a couple of fascinating things to talk about 0:19:38.840 --> 0:19:41.520 in each of these kinds of anesia. We'll start with 0:19:41.640 --> 0:19:46.359 retrograde anesia, where you lose your past memories. The fascinating 0:19:46.400 --> 0:19:49.840 thing is that scientists aren't really sure if you actually 0:19:49.920 --> 0:19:51.480 lose your memories. 0:19:52.800 --> 0:19:54.600 Yeah, so this is a question that a lot of 0:19:54.640 --> 0:19:57.560 memory scientists have what does it actually mean to have 0:19:57.840 --> 0:20:01.600 loss of memory? And so the one hypothesis is that 0:20:02.000 --> 0:20:04.600 the places in the brain where the memories are stored 0:20:04.800 --> 0:20:08.359 are damaged and so those memories are gone. And another 0:20:08.440 --> 0:20:11.400 hypothesis that you're getting at is that the memories are 0:20:11.480 --> 0:20:15.119 still stored somewhere in the brain, but via damage to 0:20:15.119 --> 0:20:17.919 the hippocampus, those memories cannot be accessed. 0:20:18.359 --> 0:20:19.920 Wow, So the memories are still. 0:20:19.760 --> 0:20:23.480 In there potentially potentially Yeah, Because remember last time we spoke, 0:20:23.520 --> 0:20:26.320 I sort of described this idea that the hippocampus in 0:20:26.359 --> 0:20:30.200 particular is a pointer to different parts of the brain 0:20:30.280 --> 0:20:32.840 where the memories are kind of stored within a network, 0:20:33.680 --> 0:20:36.480 and so when that index pointer is not working anymore, 0:20:36.600 --> 0:20:39.920 those memories are not accessible. Now we don't know for sure, 0:20:40.000 --> 0:20:41.960 because there's a lot about memory and the brain that 0:20:42.000 --> 0:20:44.920 we don't yet understand, but that is one idea that's 0:20:44.920 --> 0:20:45.760 been put out there. 0:20:47.040 --> 0:20:50.480 Yes, if you have retrograde amnesia, your memories might still 0:20:50.520 --> 0:20:53.600 be intact in your brain and what you lose is 0:20:53.680 --> 0:20:57.560 actually the ability to access them, although that doesn't mean 0:20:57.600 --> 0:20:59.000 you could get them back. 0:21:00.480 --> 0:21:03.919 Some cases, like in soap operas for example, sometimes it 0:21:03.920 --> 0:21:06.640 does involve an injury to the head, and so you'll 0:21:06.640 --> 0:21:10.200 see a situation where somebody got bonked on the head. 0:21:10.600 --> 0:21:13.359 They can't remember anything, including who they are, for a 0:21:13.400 --> 0:21:15.840 period of time, and then oftentimes they get bonked on 0:21:15.880 --> 0:21:18.800 the head again and that sort of shakes them out 0:21:18.840 --> 0:21:22.680 of the amnesic syndrome. And so that's not an accurate 0:21:22.680 --> 0:21:24.720 depiction of what looks like. 0:21:24.920 --> 0:21:29.240 Oh no. Now, for people with anterograde amnesia, or the 0:21:29.359 --> 0:21:33.200 inability to make new memories, there are two fascinating things 0:21:33.200 --> 0:21:36.080 about them. The first is that because they can't make 0:21:36.160 --> 0:21:40.560 new episodic memories, they live in a constant state of surprise, 0:21:40.840 --> 0:21:43.199 as if they are just waking up every so often, 0:21:43.400 --> 0:21:47.000 because anything that's happened to them recently they don't remember. 0:21:48.359 --> 0:21:50.720